Silver base alloy for making electrical contacts



Nov. 11,. 1969 K. R. COMEY, JR,, ET AL 3,477,845

SILVER BASE ALLOY FOR MAKING ELECTRICAL CONTACTS Filed Jan. 5, 1967 United States Patent 3,477,845 SILVER BASE ALLOY FOR MAKING ELECTRICAL CONTACTS Kenneth R. Comey, Jr., Norwood, Mass, and George Durst, deceased, late of Attleboro, Mass., by John W. McIntyre and Edmund F. Henry, administrators, Attleboro, Mass., assignors to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Jan. 3, 1967, Ser. No. 607,081 Int. Cl. C22c /00 US. Cl. 75-173 4 Claims ABSTRACT OF THE DISCLOSURE Improved alloys of cadmium oxide and silver are produced by incorporating therein between 0.001% and 0.5% by weight of mercury as an additive. Electrical contacts formed from such alloys exhibit less arc-erosion without substantial increase in contact resistance as compared with electrical contacts formed from cadmium oxide-silver alloys having cobalt incorporated therein as an additive.

This invention relates to an improved silver-cadmium oxide alloy for making electrical contacts and to electrical contacts made therefrom.

Among the several objects of the invention may be noted the provision of an improved silver base alloy for making improved electrical contacts, said contacts having reduced arc-erosion; and the provision of an alloy of the class described which has adequately low contact resistance. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the ingredients, combinations of ingredients, the proportions thereof and features of composition, the steps and sequence of steps, and features of operation, which will be exemplified in the product and methods hereinafter described, and the scope of the applicability of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a view of stock in the form of a rod made of the improved alloy of the invention and showing two blanks as cut from the rod;

FIG. 2 is a view of electrical contacts formed by one of the blanks shown in FIG. 1; and

FIG. 3 is a perspective view of an alternate form of the invention.

The invention is an improvement upon alloys and electrical contacts such as described in U.S. Patent 2,932,595. As is known in the art and from said patent, silver has been alloyed with cadmium, with the addition of cobalt for making electrical contacts. In general, the silver, cadmium and the additive cobalt were melted together and poured into suitable molds to form billets or ingots from which stock bars, rods and the like were made by rolling, drawing or the like. The stock was heated in air or other suitable oxygen bearing atmosphere for a suflicient time to oxidize the cadmium to cadmium oxide. This produced a material with a reduced tendency toward arc erosion. This results from the strengthening of the molten silver by the dispersed particles of cadmium oxide. This strengthening effect is increased with decreasing particle size. The cobalt additive functions to decrease particle size thereby reducing contact are erosion and contact sticking.

We have discovered two additives that, together with the internally oxidized cadmium oxide in the silverice cadmium alloy, produce a completed alloy having further improved arc-erosion properties when formed as an electrical contact, without substantial increase in contact resistance. Although the cost of these additives is considerable, their superiority over cobalt or other additives we have discovered makes their use worthwhile. One form of the invention consistsin melting cadmium (Cd) silver (Ag), and ruthenium (Ru) as an additive and then pouring the melt to form an ingot. The ingot is then reduced by rolling, drawing or the like to form a suitable stock, one form of which may be a rod 1 as illustrated in FIG. 1. The stock is then subjected to heating from one to several hours in an oxygen bearing atmosphere at an elevated temperature, for example 1500" F. Time and temperature are subject to variation but they should be sufiicient to oxidize the cadmium in a reasonable time, taking into account such factors as the thickness of the stock, the melting temperature and the like. The cadmium then takes the form of a multiplicity of cadmium oxide particles dispersed through the matrix of silver containing the ruthenium additive. The ruthenium additive acts in a manner similar to but improved over that of cobalt and effects improved arc erosion characteristics with improved or equal contact resistance. From segments 3 of the stock contacts are formed such as shown at 5 in FIG. 2, for example. The contacts may be formed by a heading machine or other suitable apparatus. In an alternate preferred procedure, the contacts 5 may be formed from the stock 1 prior to the oxidization step so that the oxidization is performed in the contacts 5 themselves.

In the alternate embodiment shown in FIG. 3, the ingot of alloy is formed into strips 7 which are bonded to layers of fine silver 9 and thereafter the strip is heated in an oxygen bearing atmosphere to internally oxidize layer 7. Thereafter the strip 7 is liquid phase bonded or soldered through soldered layers 11 to a base metal strip 13 formed for example of brass, beryllium copper, Phosphor bronze or the like. Finally individual contact assemblies 15 may be formed from the strip.

A preferred formulation of the stock 1 on strip 7 in proportions by weight is approximately 15% cadmium oxide, 0.01% ruthenium, the balance silver. A suitable range for the cadmium oxide component is approximately 1.0%20.0% and for the ruthenium component approximately 0.001 %-0.5%. A contact such as shown at 5 in FIG. 2 made from a workpiece such as 3 of FIG. 1 or as shown at 15 of FIG. 3 exhibits much less arcerosion without substantial increase of contact-resistance, as compared with the alloy of said patent containing a cobalt additive.

Another additive within the purview of our invention is mercury (Hg). A preferred formulation in proportion by weight is approximately 15 cadmium oxide, 0.01% mercury, the balance silver. A suitable range for the cadmium oxide component is approximately 1.0%- 20.0% and for the mercury component approximately 0.001%-0.5%, the balance silver.

It will be understood that the silver, cadmium or mercury and ruthenium may contain a degree of impurities such as is found in commercial or reagent grades of these materials. The impurities are not the additives described herein.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above composition, articles and methods without departing from the scope of the invention, it is intended that all matters contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and References Cited not in a limiting sense. UNITED STATES PATENTS What is claimed is: 5 173 1. An alloy consisting essentially of between approxi- 2:058857 10/1936 Emmert 7 mately 1.0% and 20.0% by weight of cadmium Oxide, 5 2,145,690 1/1939 12199581 75 173 between approximately 0.001% and 0.5% by weight of 2,241362 5/1941 Kelte] 200 166 mercuwthe balancesilven 2,319,259 5/1943 Peterson 200166 2. An electrical contact formed of the alloy set forth 2,539,298 1/1951 P et aL 75*173 X in claim 2,796,495 6/1957 Keitel et a1. 200166 3. An alloy consisting essentially of approximately 10 15.0% cadmium oxide, 0.01% mercury, the balance CHARLES N'LOVELLPnmary Exammer silver.

US. Cl. X.R. 4. An electrical contact formed of the alloy set forth 148 32; 200 166 in claim 3. 

